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1.
Coesite in suevite from the Ries impact structure (Germany): From formation to postshock evolution 
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下载免费PDF全文 Agnese Fazio Ulrich Mansfeld Falko Langenhorst 《Meteoritics & planetary science》2017,52(7):1437-1448
Coesite is one of the most common and abundant high‐pressure phases occurring in impactites. The mechanism of formation of coesite and its postshock evolution is revisited in this paper based on Raman microspectroscopy, and scanning and transmission electron microscopy of a coesite‐bearing suevite from the Ries impact structure. Our data indicate that coesite forms through a single process, i.e., by crystallization from high‐pressure silica melt, and that its formation is related to fluid inclusions in precursor quartz. During the postshock phase, coesite aggregates are partially modified by annealing and interactions with fluids. In an early stage of the postshock evolution, coesite is back‐transformed to quartz and the surrounding diaplectic glass devitrifies into β‐cristobalite, which transforms into α‐cristobalite and then into microcrystalline quartz during subsequent stages of the postshock evolution. Altogether these postshock modifications result in a significant volume loss and extensional fracturing. During a late postshock stage, the fractures are filled with clay minerals due to circulation of hydrothermal fluids. 相似文献
2.
summary . Calculations of the thermodynamical Gruneisen's gamma as a function of temperature and volume for iron are presented. The ranges of the relevant pressures and temperatures extend to those corresponding to the Earth's core. The various crystal structures of iron and several kinds of inter-molecular potential functions are considered. It is found that it is not possible to describe the Gruneisen's gamma for iron with the accuracy needed for an assessment of the thermal state of the core mainly because the available experimental data do not allow a definite choice among the possible potential functions. 相似文献
3.
Using a hydrodynamic model of protogalactic evolution, we explain the amount of iron in rich clusters, deduced from X-ray observations. In fact, our calculations show that a strong shock wave originates in the first violent collapse phase and leaves the protogalaxy, carrying out a substantial fraction of its mass, with roughly solar metallicity and high temperature (107–108 K). We also show that hot material ejected from proto-cD galaxies can probably explain the observed X-ray emission in clusters. 相似文献
4.
Fazio Eugenio Punturo Rosalda Cirrincione Rosolino Kern Hartmut Pezzino Antonino Wenk Hans-Rudolf Goswami Shalini Mamtani Manish A. 《International Journal of Earth Sciences》2017,106(7):2259-2278
International Journal of Earth Sciences - In the geologic record, the quartz c-axis patterns are widely adopted in the investigation of crystallographic preferred orientations (CPO) of naturally... 相似文献
5.
Md. Salah U. Sharif Ralph K. DavisKenneth F. Steele Burmshik KimPhillip D. Hays Tim M. KresseJohn A. Fazio 《Applied Geochemistry》2011,26(4):496-504
The potential health impact of As in drinking water supply systems in the Mississippi River Valley alluvial aquifer in the state of Arkansas, USA is significant. In this context it is important to understand the occurrence, distribution and mobilization of As in the Mississippi River Valley alluvial aquifer. Application of surface complexation models (SCMs) to predict the sorption behavior of As and hydrous Fe oxides (HFO) in the laboratory has increased in the last decade. However, the application of SCMs to predict the sorption of As in natural sediments has not often been reported, and such applications are greatly constrained by the lack of site-specific model parameters. Attempts have been made to use SCMs considering a component additivity (CA) approach which accounts for relative abundances of pure phases in natural sediments, followed by the addition of SCM parameters individually for each phase. Although few reliable and internally consistent sorption databases related to HFO exist, the use of SCMs using laboratory-derived sorption databases to predict the mobility of As in natural sediments has increased. This study is an attempt to evaluate the ability of the SCMs using the geochemical code PHREEQC to predict solid phase As in the sediments of the Mississippi River Valley alluvial aquifer in Arkansas. The SCM option of the double-layer model (DLM) was simulated using ferrihydrite and goethite as sorbents quantified from chemical extractions, calculated surface-site densities, published surface properties, and published laboratory-derived sorption constants for the sorbents. The model results are satisfactory for shallow wells (10.6 m below ground surface), where the redox condition is relatively oxic or mildly suboxic. However, for the deep alluvial aquifer (21-36.6 m below ground surface) where the redox condition is suboxic to anoxic, the model results are unsatisfactory. 相似文献
6.
The precipitation/replacement of Ca‐phosphate is a complex process that commonly takes place during the early diagenesis in marine sediments. The unusual occurrence of shallow marine, early diagenetic phosphatic deposits associated with glassy tuffs in the Neogene Gaiman Formation, in the Chubut Province, Patagonia, Argentina, constitutes a good case example for the study of replacement and precipitation of Ca‐phosphate on an unstable substrate. Isocon diagrams illustrate that chemical changes during glass diagenesis include gains in loss on ignition and Ca, and losses of K. These changes are the result of glass hydration during sea water–glass interaction, together with adsorption and diffusion of ions into the bulk shard; combined, these represent an incipient process of volcanic glass replacement by Ca‐phosphate. Subsequent early diagenetic P enrichment in the pore solutions led to phosphate precipitation, associated with pitting on the glass shards and pumice. The associated development of a reactive surface promoted the incorporation of P and Ca into their margins. Lastly, precipitation of calcium phosphate filled the vesicles and other open cavities, inhibiting further glass dissolution. The high porosity and reactivity of the volcanic glass provided an appropriate substrate for phosphate precipitation, leading to the development of authigenic apatite concretions in the volcanic‐glass bearing strata of the Gaiman Formation. This research is of significance for those concerned with marine phosphatic deposits and sheds light on the processes of early diagenetic phosphate precipitation by replacement of an atypical, unstable substrate like hydrated volcanic glass. 相似文献
7.
Rosolino Cirrincione Eugenio Fazio Patrizia Fiannacca Gaetano Ortolano Rosalda Punturo 《Pure and Applied Geophysics》2009,166(5-7):995-1010
In order to reveal any correlation between the preferred orientation of quartz and progressive intensity of strain, a suite of deformed leucogneiss collected within a ductile shear zone outcropping in Calabria (southern Italy) was investigated. Based on the microstructural approach and matrix-clast relationships, the method applied here may be useful for appraising the connection between deformation mechanisms of constituent minerals and bulk textural properties of naturally sheared rocks. Accordingly, quartz c-axis orientation patterns were determined by image-assisted analysis. Results revealed a correlation between finite strain and textural features: As strain increases, the matrix develops at the expense of the clast counterpart, which is instead progressively reduced in both size and amount. 相似文献
8.
Christopher Hamann Agnese Fazio Matthias Ebert Lutz Hecht Richard Wirth Luigi Folco Alex Deutsch Wolf Uwe Reimold 《Meteoritics & planetary science》2018,53(8):1594-1632
We have investigated silicate emulsions in impact glasses and impact melt rocks from the Wabar (Saudi Arabia), Kamil (Egypt), Barringer (USA), and Tenoumer (Mauritania) impact structures, and in experimentally generated impact glasses and laser-generated glasses (MEMIN research unit) by scanning electron microscopy, electron microprobe analysis, and transmission electron microscopy. Textural evidence of silicate liquid immiscibility includes droplets of one glass disseminated in a chemically distinct glassy matrix; sharp phase boundaries (menisci) between the two glasses; deformation and coalescence of droplets; and occurrence of secondary, nanometer-sized quench droplets in Si-rich glasses. The compositions of the conjugate immiscible liquids (Si-rich and Fe-rich) are consistent with phase separation in two-liquid fields in the general system Fe2SiO4–KAlSi3O8–SiO2–CaO–MgO–TiO2–P2O5. Major-element partition coefficients are well correlated with the degree of polymerization (NBO/T) of the Si-rich melt: Fe, Ca, Mg, and Ti are concentrated in the poorly polymerized, Fe-rich melt, whereas K, Na, and Si prefer the highly polymerized, Si-rich melt. Partitioning of Al is less pronounced and depends on bulk melt composition. Thus, major element partitioning between the conjugate liquids closely follows trends known from tholeiitic basalts, lunar basalts, and experimental analogs. The characteristics of impact melt inhomogeneity produced by melt unmixing in a miscibility gap are then compared to impact melt inhomogeneity caused by incomplete homogenization of different (miscible or immiscible) impact melts that result from shock melting of different target lithologies from the crater's melt zone, which do not fully homogenize and equilibrate due to rapid quenching. By taking previous reports on silicate emulsions in impact glasses into account, it follows that silicate impact melts of variable composition, cooling rate, and crystallization history might readily unmix during cooling, thereby rendering silicate liquid immiscibility a much more common process in the evolution of impact melts than previously recognized. 相似文献
9.
Microscopic impactor debris in the soil around Kamil crater (Egypt): Inventory,distribution, total mass,and implications for the impact scenario 下载免费PDF全文
下载免费PDF全文 Luigi Folco Massimo D'Orazio Agnese Fazio Carole Cordier Antonio Zeoli Matthias van Ginneken Ahmed El‐Barkooky 《Meteoritics & planetary science》2015,50(3):382-400
We report on the microscopic impactor debris around Kamil crater (45 m in diameter, Egypt) collected during our 2010 geophysical expedition. The hypervelocity impact of Gebel Kamil (Ni‐rich ataxite) on a sandstone target produced a downrange ejecta curtain of microscopic impactor debris due SE–SW of the crater (extending ~300,000 m2, up to ~400 m from the crater), in agreement with previous determination of the impactor trajectory. The microscopic impactor debris include vesicular masses, spherules, and coatings of dark impact melt glass which is a mixture of impactor and target materials (Si‐, Fe‐, and Al‐rich glass), plus Fe‐Ni oxide spherules and mini shrapnel, documenting that these products can be found in craters as small as few tens of meters in diameter. The estimated mass of the microscopic impactor debris (<290 kg) derived from Ni concentrations in the soil is a small fraction of the total impactor mass (~10 t) in the form of macroscopic shrapnel. That Kamil crater was generated by a relatively small impactor is consistent with literature estimates of its pre‐atmospheric mass (>20 t, likely 50–60 t). 相似文献
10.
Thomas L. De Fazio 《Tectonophysics》1974,23(1-2)
Geophysical data describing the geometry of underthrust crustal plates at the island arcs are fitted to the relation for strain-free buckling of a thin spherical shell as given by Frank (1968). Agreement of this relation with the data is notable for extensive arcs of large radius. The geometry associated with arcs of smaller radius is less strongly constrained and the dip of descending plates at arcs of small radius is greater than that predicted by the buckling relation. The data have implications concerning the growth of island arcs and the direction in which they may develop. 相似文献